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Fiber optic communication started to develop very quickly after the production of the first low-loss single-mode silica fibers and the invention of the semiconductor laser diode around 1970. In the late 1970s until the middle of 1990, fiber transmission capacity roughly doubled each year.
The increasing demand for higher network capacity, which is driven to a high degree by the continuous rapid growth of the Internet, provides a great challenge for telecommunication network providers. To satisfy this demand, the networks are moving more and more to dense wavelength-division-multiplexed (DWDM) systems. A considerable increase in bandwidth per fiber has become possible with the development of erbium-doped fiber amplifiers (EDFAs).
The single-fiber bandwidth depends on the bit rate of transmitted information on each wavelength and the number of wavelengths being carried. Either increasing the data rate on each wavelength channel or increasing the number of wavelength channels can increase the capacity. Broadening the available spectrum in a system or decreasing the spectral separation of wavelength channels, or both, increases the channel count.
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